Conventionally, projectors having a plurality of optical modulators (liquid crystal panels) for respectively modulating a plurality of color lights in accordance with image information, a color combining optical system (cross dichroic prism) for combining respective color lights modulated by the optical modulators, and a projection optical system (projection lens) for enlarging and projecting the light beam combined by the color combining optical system have been used.
Among such projectors, so-called three-plate type projectors have been known, in which a light beam irradiated from a light source is separated into three color lights of red, green and blue by dichroic mirrors, the respective color lights are modulated by three liquid crystal panels in accordance with image information, and the modulated light beams are combined by a cross dichroic prism to form a color image enlarged and projected through a projection lens.
In order to obtain a clear projection image by such projectors, focus adjustment and alignment adjustment of the respective liquid crystal panels must be performed with high accuracy to prevent the pixel-deviation between the respective liquid crystal panels and the deviation in the distance from the projection lens. Here, the focus-adjustment is an adjustment for precisely disposing each respective liquid crystal panel at the back-focus of the projection lens, and the alignment-adjustment is an adjustment for aligning the pixels of the respective liquid crystal panels, which also apply to the description below.
Conventionally, the focus and alignment adjustments of liquid crystal panels are performed on an optical device having three liquid crystal panels and a cross dichroic prism, in accordance with the steps of: (1) irradiating a light beam on an image formation area of the respective liquid crystal panels; (2) detecting the light beam, which is irradiated on the light-incident surface of the cross dichroic prism and then irradiated from the light-irradiation surface with a light-beam detector such as a CCD camera; and (3) adjusting the relative position of each liquid crystal panel while checking the focus and pixel position of each liquid crystal panel detected by the light-beam detector.
Among the detecting methods using a CCD camera, one method to be employed is so-called a master lens method, in which a standard projection lens (master lens) is previously installed on a manufacturing apparatus, the light beam passing through the optical device and the projection lens is projected on the screen, and the projection image is imported; and another method is so-called direct-view method, in which the light beam passing through the optical device is directly imported. By using the above methods, the optical device can be manufactured independently without installing a projection lens thereon, so that the optical device can be manufactured efficiently.
However, in the former method, due to the deviation in the image condition on the back focus position and the axial chromatic aberration, etc. between the master lens and the projection lens combined with the optical device, even if the focus and alignment of the liquid crystal panels are adjusted with high accuracy relative to the master lens, a clear image may not be obtained depending on the projection lens to be combined.
Similarly, in the latter method, after combining a projection lens with the optical device to produce the projector, if the optical property values of the combined projection lens go outside the reference value range, even if the focus and alignment of liquid crystal panels is adjusted with high accuracy, a clear image may not be obtained.